This invention relates to the field of modular housing, and particularly modular construction techniques and methods as developed for a modular log structure.
Log cabins and other structures have been in existence for centuries. Initially, such structures were built in proximity to softwood forests which provided ready and easily harvested source of building materials which could be utilized with a minimum number of finishing operations and erected using manual labor. In modern times, log cabins have been recognized as highly versatile, energy efficient structures, and a wide variety of log structures and construction techniques have been developed over the last century.
By way of example, U.S. Pat. No. 1,445,738 discloses a "portable bungalow" constructed of interlocked prefabricated wall sections of vertical half-logs. U.S. Pat. No. 1,902,309 discloses another log structure of vertical half-logs, this time using facing rows of overlapped half-logs, as does U.S. Pat. No. 1,980,309, the latter patent placing rows of half-logs on the inside and outside of a thin, centrally disposed wall.
In more modern times, other attempts have been made to construct or simulate the construction of a log structure. U.S. Pat. Nos. 4,115,969, 4,463,552 and 4,807,413 disclose various prefabricated log wall panels which are then assembled on-site into a log structure via different fastening techniques. U.S. Pat. Nos. 4,305,238 and 4,640,069 disclose techniques for simulating the appearance of log structures; U.S. Pat. No. 4,147,000 discloses a double wall log structure with insulation between the walls. Finally, U.S. Pat. Nos. 3,908,322 and 4,787,185 disclose log construction techniques utilizing interlocked logs cut and/or milled in particular patterns for speedy and easy assembly on site as well as lower air infiltration, greater weather-tightness, less warpage, etc.
All of the foregoing patents require a substantial amount of on-site assembly manpower and, consequently, time. In addition, final assembly on-site depends in large part on the skill of a local building contractor's work crew, which varies widely and may, in many instances, unfortunately result in a substandard end product. In addition, in many of the more northern latitudes where log homes are extremely popular due to their aforementioned energy efficiency, hostile weather conditions result in a very short building season, and an on site construction crew is limited to a few "stick built" structures each season. Essentially, the log home industry has traditionally suffered from its inability to utilize modular construction techniques which have been applied for years to frame type modular construction.
The reasons for the above limitation are inherent in the use of logs as building materials. Except in rare instances, logs of adequate diameter (usually 6-24 inches) are limited to a maximum of 16-20 feet in length. In addition, walls constructed of log courses are extremely heavy in comparison to a conventional framed wall of 2.times.4 studs. Very small log structures have in the past been preassembled and moved as a unit to an installation site, but such are limited to no more than 15 or 20 feet on a side because of the tensile and shear stresses imposed on a log wall when lifted from below by jacks, slings or cables at a few discrete lifting points. As a log wall becomes longer, the buckling tendencies of this point-type lifting are aggravated by the increased weight of the wall and the fact that the wall cannot be built of a single log from end to end, but must be constructed of several butted logs in each course. Further aggravating the strength problem of such a wall are the necessary windows and doors extending therethrough. Of course, a log structure could be jacked up, placed on rails and moved in one piece down a street or highway on wheeled carriages, as older homes are sometimes moved, but this technique is time consuming, expensive, and requires special permits and road closings to accommodate the width of the structure. Therefore, such a technique is obviously impractical for long distance transport or transport to remote building sites in mountain country accessible only by gravel or even dirt roads.